Answer: 8 years ago
Explanation:
w = woman's age
d = daughter's age
Hypothetically, find the woman's age eighteen years ago when the daughter is 1 year old.
(18 years ago):
w = 20 + 3d
w = 20 +3(1)
w = 23
The woman is 23 years old.
Now, find the age of the daughter 18 years ago when the woman is three times her age:
w + x = 3(d + x)
**x is the number of years that pass, so it needs to be added to the raw age of the woman and her daughter. That's why it's inside the parenthesis.**
w + x (- x) = 3d + 3x (- x)
w = 3d + 2x
(23) = 3(1) + 2x
**Now, we plug in the initial raw ages to find the number of years that have passed.**
20 = 2x
x = 10
18 - (10) = 8 years ago
Since our math took place 18 years ago, we fast-forward 10 years, making the woman 3 times older than her daughter 8 years ago.